All of the roof air units are going to be noisy. For the minimal difference in cost, I would go with the larger unit. Bigger is better because the units are not that efficient and trailers are poorly insulated. You'll need all you can get. Stay with the major manufacturers, Dometic, or Coleman.
2013 F250 XLT
I now have a Keystone Outback, but I try to help when I can.
Bitter Gun Owner